In a known centrifugal separator of this kind the passage from the separation chamber opens into the outlet chamber at a level radially inside the free liquid surface. In the outlet chamber a number of wings extending axially and radially are fixed to the walls defining of the outlet chamber. A separated liquid entering the outlet chamber is thrown radially outwardly and collides either directly with the free liquid surface or with one of said wings thereafter to be thrown further radially outwardly to the free liquid surface. The flow of the separated liquid radially outwardly in the rotating liquid body to the inlet of the outlet channel mainly takes place in thin layers along the wings and one of the end walls of the outlet chamber.
The described collision between the separated liquid and the free liquid surface, or between the liquid and a wing, result in splashes, which means there is a great risk of air or gas, located radially inside the free liquid surface in the outlet chamber, being admixed in the separated liquid, which flows radially outwardly to the inlet of the outlet channel and then to the outlet. Also the locally high liquid flow velocity, which occurs in the layers of the liquid body the free liquid surface, in which the liquid flows radially outwardly, results in a great risk of such an admixture of air or gas.
In order to decrease the high liquid flow velocities in the layers in which the liquid flows radially outwardly it has been suggested, as shown in WO 89/03250 A1, that the means, which in the outlet chamber is to entrain the liquid into the rotation of the rotor, is designed as at least one disk concentrically fixed to the rotor. By this means, the outwardly directed liquid flow in the outlet chamber is distributed in more layers having a large total cross-sectional area, whereby the flow velocities in the layers and consequently the risk of air admixture decreases. However, the disc or discs according to this suggested solution is not capable of decreasing the air admixture sufficiently and at at the same time satisfactorily entraining the separated liquid in the rotation of the rotor.